Die Hard: ETC's First Independent Network Upgrade

At block 3,000,000 on January 13, 2017, the Die Hard network upgrade activated — the first network upgrade specific to Ethereum Classic, marking the network's protocol independence from Ethereum. Die Hard was specified in ECIP-1010.

## Included Changes

- **ECIP-1010 — Delay Difficulty Bomb**: Paused the exponential difficulty growth between blocks 3,000,000 and 5,000,000. The bomb formula (2^(floor(block/100000) - 2)) was producing noticeable block time increases. This delay bought time for the community to decide the bomb's permanent fate — it was later removed entirely in ECIP-1041.
- **EIP-155 — Replay Protection (Chain ID 61)**: Added a chain identifier parameter to transaction signatures. Before Die Hard, a transaction signed on ETC could be replayed on ETH (and vice versa), since both chains shared the same transaction format. Chain ID 61 for ETC (vs. 1 for ETH) made transactions chain-specific, eliminating this persistent security risk.
- **EIP-160 — EXP Cost Increase**: Increased the EXP opcode cost from 10 to 50 gas per byte of exponent. The original pricing underestimated the computational cost of large exponentiation operations.
- **EIP-161 — State Trie Clearing**: Enabled removal of empty accounts from the state trie. Cleaned up accounts created during the 2016 Shanghai DoS attacks that had bloated state storage.

## Significance

Die Hard was a sovereignty decision. By implementing Chain ID 61, ETC established a permanent cryptographic boundary between itself and Ethereum. Replay protection eliminated the most urgent cross-chain security risk, and the difficulty bomb delay initiated the process that would eventually lead to ETC permanently removing the bomb — affirming proof-of-work as the network's consensus mechanism.